1. Field of the Invention
The present invention relates to a projection exposure apparatus for forming fine patterns required for manufacture of LSIs.
2. Description of the Related Art
FIG. 9 shows an optical system of a conventional projection exposure apparatus. The optical system includes a lamp house 1, a mirror 2, a fly's eye lens 3 disposed in front of the lamp house 1 with the mirror 2 between the lamp house 1 and the fly's eye lens 3 an aperture member 4 located in front of the fly's eye lens 3, a relay lens 5A, a stop 6, a mirror 7, a condenser lens 5B, a photo mask 8 on which a circuit pattern is formed, a projection lens 9, and a wafer 10 located in front of the mask 8 with the projection lens 9 between the mask 8 and the wafer 10.
Light rays emanating from the lamp house 1 reach the fly's eye lens 3 through the mirror 2, and are split into regions by the individual lenses 3a of the fly's eye lens 3. The rays which have passed through the individual lenses 3a pass through an aperture portion 4a of the aperture member 4, the relay lens 5A, the stop 6, the mirror 7 and the condenser lens 5B, and illuminate the entire surface of the exposure area of the mask 8. Therefore, on the surface of the mask 8, the rays from the individual lenses 3a of the fly's eye lens 3 are laid on top of one another, and the mask 8 is thus uniformly illuminated. The light rays which have passed through the mask 8 in the manner described above pass through the projection lens 9 and then reach the wafer 10. A resist film on the surface of the wafer 10 is exposed to this illumination light, whereby transfer of the circuit pattern is achieved.
As a result, a resist pattern 22 such as that shown in FIGS. 10 and 11 is formed on the surface of the wafer 10. At that time, various types of shoulders 23 are present on the surface of the wafer 10 as a consequence of circuit formation. Therefore, light L1 which illuminates the vicinity of an edge of the shoulder 23 is reflected in a oblique direction by an inclined surface 23a part of this edge, causing halation. Consequently, the portion of the resist located near the edge is excessively exposed to the light, whereby a concavity 24 is formed in the resist pattern 22. Thus, in a conventional exposure apparatus, the resist dimension accuracy deteriorates due to halation.